The present invention is directed to fiber optical transport systems. More particularly, an embodiment of the invention provides a compact, low-cost, integratable solution for monitoring individual optical power in a DWDM transmitter array integrated on a planar lightwave circuit (PLC) platform. Merely by way of example, the invention provides a method for using weak refractive index gratings formed on a silica/silicon waveguide to redirect a portion of the optical power vertically out of the transmission medium for detection by a photodiode flip-chip bonded on the PLC above the grating. But it would be recognized that the invention has a much broader range of applicability.
Considerable effort has been devoted to the development of compact, low-cost transmitters for dense wavelength division multiplexing (DWDM) applications since early 1990s. One of the promising approaches is to integrate semiconductor lasers, optical taps, and silica-based waveguide devices such as arrayed waveguide grating (AWG) or couplers, together to have a 1×N DWDM transmitter array. Compared to discrete devices, this approach eliminates fiber jumpers between transmitters and the MUX unit. Also, instead of packaging each transmitter and MUX individually with their own physical cases and fiber pigtails, this hybrid integration uses only one box with significantly low number of pigtails. In addition, the physical size of the transmitter array is much smaller than those made with discrete devices, increasing considerably the port density.
Even though these conventional DWDM systems are useful in some areas, they have many limitations that restrict their effectiveness in broader applications. Some of these limitations are discussed below, and then improved techniques based on embodiments of the present invention are provided.